a) Field of the Invention
The present invention relates to propylene copolymers having a syndiotactic structure, Preparation of the same and resin compositions containing the same. More particularly, it relates to propylene copolymers having --OH group in the side chain, which copolymers have high syndiotacticity, processes for producing the syndiotactic propylene copolymers and resin compositions containing one or more of the copolymers.
b) Description of the Prior Art
Polyolefins are low-priced and have relatively excellent physical properties. However, as having no polar group, they have some problems that the gas-barrier property is poor and the adhesiveness to polar group-having polymers is poor. In order to overcome the problems, a polar group-having polymer may be added to such a polyolefin. However, in general, the addition of such a polymer involves another problem that polar group-having polymers could hardly be blended with polyolefins and the resulting blend would often lose the physical properties inherent in polyolefins.
The existence of syndiotactic polypropylene has been known for many years. However, polypropylene obtained by a conventional low-temperature polymerization method of using a catalyst comprising a vanadium compound, ether and an organoaluminium compound has poor syndiotacticity so that it can hardly be considered to have the characteristic properties as syndiotactic polypropylene. On the other hand, where ordinary olefin polymerization catalysts are used, olefins having polar groups such as --OH are not almost polymerized. Under the situation, polar group-having stereoregular polyolefins have heretofore been unknown.
J. A. Ewen et al. found that polypropylene having such good tacticity as exceeding 0.7 in terms of syndiotactic pentad fraction can be obtained by polymerizing propylene in the presence of a catalyst comprising a transition metal compound having asymmetric ligands and an aluminoxane (J. Am. Chem. Sot., 1988, 110, 6255-6256). T. C. Chung reported that a propylene-alkenyl alcohol copolymer having an isotactic structure can be obtained by oxidizing and decomposing a propylene copolymer composed of an alkenylborane and propylene and having an isotactic structure (Macromolecules, 1988, 21, 865).
Copolymers having a substantially syndiotactic structure and having --OH group in the side chain have heretofore been unknown. Such copolymers are expected to have physical properties which could not be seen in any conventional copolymers, and compositions containing such copolymers are also expected to have physical properties which could not be seen in any conventional compositions.